The invention is related to a device on hand machine tools.
Such a device is already known from DE-PS 25 51 125. Tools constructed according to this patent are also usable in principle in tool receptacles provided according to AT-PS 285 405, wherein the locking elements applied in the latter engage in the recesses which are closed on both sides and arranged in the tool shaft outside the rotary driving grooves. The width and depth of the rotary driving grooves opening out at the end of the tool shaft are selected in such a way that they can not receive the locking elements, and accordingly the tool can not be incorrectly inserted.
However, particularly in severe construction site operation, the rotary driving grooves can become worn out after long use of the tool to such an extent that the tool can unintentionally be inserted into the tool holder in a position in which the locking elements engage in the rotary driving grooves. This brings about the risk that the machine may be unexpectedly disengaged from the tool when withdrawing the machine from the workpiece during operation, since the locking elements of the tool receptacle can slide out of the rotary driving grooves, which are open toward the end of the tool, in an unimpeded manner. This is particularly dangerous because when working with the machine the operator can not determine in certain cases that the tool is incorrectly inserted. In this case, the operator will only notice it--but in an entirely unanticipated manner--when he withdraws the machine from the workpiece and the tool, which is possibly stuck in the workpiece, remains in the latter. Since this separation of machine and tool is entirely unanticipated by the operator, there is the danger that he will lose his balance when working on a ladder or scaffold, which brings about a considerable risk of accident.